The invention relates to a method for operating an electrically driven motor vehicle with a battery-fed electric drive motor and a generator-coupled internal combustion engine for providing electric energy for the electric drive motor or, more specifically, the battery. In this case the internal combustion engine is operated (REX operating mode) based on the state of charge of the battery. Furthermore, the invention relates to a device for carrying out such a method.
Such a method is known from DE 10 2008 059 199 A1, which describes an electric vehicle that has a so-called range extender and that is driven exclusively by an electric machine. Furthermore, there is a low-power internal combustion engine with a coupled generator for recharging the battery.
The cruising range of battery operated electric vehicles creates a general feeling of uneasiness among users, because unlike fuel-driven vehicles, where it is possible to extend any cruising range by refueling with minimal effort and time and with a broad range of availability, the high voltage battery of electric vehicles can be charged only in a few places. In addition, the charging process requires considerably more time than the refueling of a motor vehicle with an internal combustion engine. This feeling of uneasiness may be intensified, for example, especially if the battery is not totally charged at the start of the trip or if longer distances have to be covered.
JP 08126116 A and JP 2000188802 A disclose a method that is intended for operating hybrid vehicles comprising electric motors and internal combustion engines and that controls the charging of the battery on the basis of navigation data.
Furthermore, it is known from the prior art to provide, in particular, energy saving operating modes that are intended for hybrid and electric vehicles and that reduce the consumption of energy in order to increase in this way the cruising range of the vehicle. Hence, it is possible to limit or totally suppress the operation of large electric power consumers, like air conditioning and heating systems, for the purpose of saving energy. Furthermore, a maximum speed limiter or an output power limiter of the electric drive motor can be activated.
To date the driver has selected these energy saving operating modes manually.
The object of the invention is to provide a method of the above-mentioned type that makes it possible for the driver of the electric vehicle to reach his destination with minimum inconvenience and without having to worry at the start of his trip about whether the destination can be reached.
The method according to the invention ensures that a driver will not be surprised that the entered destination will not be reached. Rather, the driver can start after entering the destination, provided that the system has not already determined at the start of the trip that even in total REX mode the destination cannot be reached. If the method according to the invention has made sure that the destination will be reached, the driver can start “contented.” Should it be determined during the processing, in particular periodic processing, of the inventive method at a later time that at this point the destination can no longer be reached—possibly due to large energy consumers, like air conditioning systems, having been activated in the interim or due to fast or more specifically sporty driving—without restricting the electric power consumers and, thus, a switch to an energy saving operating mode is recommended, then the driver may or may not comply with this recommendation. If the driver follows the recommendation, then the selected energy saving operating mode is implemented, and the destination will be reachable again. If, in contrast, the driver does not follow the recommendation, for example a weaker energy saving operating mode than recommended is selected, then this is implemented, even if this mode will not close the range gap and, thus, the destination would not be reached. The situation is the same, preferably if the driver does not react to the recommendation at all, thus, no change in state. Not until the method according to the invention later determines that the destination cannot be reached without the REX operating mode does the system automatically switch over to the REX operating mode, in which a portion of the energy consumed by the electric motor is provided by the internal combustion engine, with the result that the range is suitably extended.
According to one advantageous further development of the invention, a maximum speed restriction is executed in the at least one energy saving mode. This feature makes it possible to reduce the specific energy demand per route owing to the decrease in air resistance, thus increasing the total cruising distance of the vehicle. As an alternative, a performance restriction can also be executed, a feature that has the advantage of being able to drive at a higher speed in the event of a tail wind or when driving downhill.
According to yet another advantageous further development of the invention, the energy consumption of an air conditioning system and/or an electric heating device is restricted in the at least one energy saving operating mode.
According to yet another advantageous further development of the invention, two or more energy saving operating modes with graduated energy saving adjustments are provided. Preferably, in a first energy saving operating mode having a smaller energy saving, the energy consumption of large consumers, like an air conditioning system, is limited and in a second energy saving operating mode is totally suppressed. It is also contemplated to let the driver gradually adjust the degree of energy restriction.
According to one advantageous further development of the invention, it is checked when determining the range gap (dRW) during REX mode, whether the recommended route runs through an environmental protection zone, in which the REX mode is inadmissible, and this is taken into consideration in determining the possible range gap (dRW). Thus, the driver does not have to worry about environmental protection zones when he is selecting the route, and/or the navigation system can determine the route accordingly and, in so doing, consider that the REX mode is prohibited in that zone. It is also possible for routes running through environmental protection zones to have the navigation system propose an alternative route that bypasses the environmental protection zones and to check whether this solution extends the range due to the possibility of a continuous REX mode or, more specifically, whether a range gap can be closed.
According to yet another advantageous further development of the invention, the energy saving operating mode is activated when the REX operating mode is activated. Thus, it is possible to increase the range even more.
One advantageous further development of the invention proposes a device that is intended for carrying out the above-described method and that includes a range management unit that can be fed the following data: (a) route data from the navigation system; (b) data about the charge level of the battery; (c) electric power consumer data about the operating state of the electric power consumers; and (d) operating state data of the electric drive motor. The range management unit may provide the following signal outputs: (a) an action recommendation signal; (b) control signals for controlling the operating mode of the electric power consumers; and (c) control signals for actuating the electric drive motor for restricting the maximum speed and/or the power output.
Both the inventive method and the necessary interactions with the driver can be carried out with such a range manager.
According to one advantageous further development of the invention, the range management unit includes an indicating and input unit, which conveys to the driver the range situation, and especially in the case of a range gap, a proposal for activating an energy saving operating mode is transmitted.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawing.